Pollen germination and hand pollination in pitaya (Hylocereus undatus)

Hand pollination is a necessary aiding method for pitaya ( Hylocereus undatus ) production to achieve a high yield. With the cultivated area of pitaya going up exponentially in the recent years, a systematic study was carried out to understand the mechanism behind the high yield. In this study, we first developed an optimal medium for the in vitro germination of pitaya pollen. Upon testing the activity of the pollen collected from or stored for different time, we observed that the relative high pollen germination rates (27.2–65.1%) were those collected at between 2 h before blooming and 6 h after blooming, the highest activity was at 2 h after blooming, and that storing them for 24 h at 4°C reduces their germination rate from 65.2% to 35.5% and their production to about 82%. Therefore, it is not appropriate to pollinate plants with pollen that have been stored for more than 24 h, without bringing a breakthrough in pollen storage. We also observed that stigma receptivity and pollen activity are synchronous, which together determine fruit setting rate and fruit size. Pollination within 6 h after blooming provides the best fruit setting percentage and fruit size, the other favorable option being pollination at 6:00 pm, that is, 2 h before blooming; however, pollination at 6:00 am the next morning is expected to lead to 23% reduction in the production. These results will be useful for reproductive biology studies in this species. Moreover, this work set an important foundation for collecting pollen and selecting the right time of hand pollination to improve the yield and breeding efficiency in pitaya.